The present invention relates generally to devices for measurement of refractive indices of fluid media, and more particularly to a practical laboratory instrument for precision measurement of the refractive index of a liquid.
The invention is a light transmissive refractive index measurement cell for liquid samples and comprises a transparent hollow cylindrical section closed at one end with a transparent flat wall element disposed transversely of the cylindrical section; one surface of the wall element includes a reference line coincident with the axis of the cylindrical section and together with the inner surface of the cylindrical section defines a sample volume of semicylindrical shape. With the sample volume empty, a light beam is projected from a source through the wall element, reference line and sample volume to a detector opposite the source to establish an angle of refraction through the empty cell. The sample volume is then filled with liquid and the angle of refraction is remeasured. The refractive index of the liquid is calculated using Snell's law.
The refractive index measurement cell of the invention may be used for rapid and accurate measurement of the refractive indices of various liquids, including liquids having intensity dependent nonlinear indices. In the observation of the beam, the refracted path of the beam is defined from the detector to the reference line through the sample volume along a radius of the semicylindrical section; no refraction occurs in the cylindrical wall of the cell, and angle measurements for the refracted beam are independent of the refractive indices of materials of construction of the cell. Residual errors are neither present in the measurements nor need be accounted for because of dimensions of component parts.
It is therefore a principal object of the invention to provide a refractive index measurement cell for liquid samples.
It is a further object to provide a laboratory device for straightforward measurement of refractive indices of liquids.
It is yet a further object to provide a device for rapid and accurate measurement of non-linear refractive indices of liquids.
These and other objects of the invention will become apparent as the detailed description of representative embodiments proceeds.